(η6-Benzene)-chlorido-[(S)-2-(4-isopropyl-4,5-di-hydro-oxazol-2-yl)phenolato]ruthenium(II).

The title compound, [Ru(C12H14NO2)Cl(η6-C6H6)], exhibits a half-sandwich tripod stand structure and crystallizes in the ortho-rhom-bic space group P212121. The arene group is η6 π-coordinated to the Ru atom with a centroid-to-metal distance of 1.6590 (5) Å, with the (S)-2-(4-isopropyl-4,5-di-hydro-oxazol-2-yl)phenolate chelate ligand forming a bite angle of 86.88 (19)° through its N and phenolate O atoms. The pseudo-octa-hedral geometry assumed by the complex is completed by a chloride ligand. The coordination of the optically pure bidentate ligand induces metal centered chirality onto the complex with a Flack parameter of -0.056.

Dimeric aluminum-phosphorus compounds as masked frustrated Lewis pairs for small molecule activation.

Hydroalumination of aryldialkynylphosphines RP(C≡C-(t)Bu)(2) (R = Ph, Mes) with equimolar quantities of diethylaluminum hydride afforded mixed alkenyl-alkynyl cyclic dimers in which the dative aluminum-phosphorus bonds are geminal to the exocyclic alkenyl groups. Addition of triethylaluminum to isolated 1 (R = Ph) or to the in situ generated species (R = Mes) caused diethylaluminum ethynide elimination to yield the arylethylphosphorus dimers 2 and 3. These possess a chair-like Al(2)C(2)P(2) heterocycle with intermolecular Al-P interactions. The boat conformation (4) was obtained by the reaction of (t)Bu-P(C≡C-(t)Bu)(2) with di(tert-butyl)aluminum hydride. Despite being dimeric, 2 behaves as a frustrated Lewis pair and activates small molecules. The reaction with carbon dioxide gave cis/trans isomeric AlPC(2)O heterocycles that differ only by the configuration of the exocyclic alkenyl unit. Four isomers resulted from the reaction with phenyl isocyanate. This is caused by cis/trans isomerization of the initial C=O adduct and subsequent rearrangement to the AlPC(2)N heterocycle, being the C=N adduct.

P-C dichotomy: divergent iron(-I)-mediated alkyne and phosphaalkyne cycloligomerisations.

In contrast to the recently reported cyclodimerisations of phosphaalkynes, alkynes preferably trimerise at the same low-valent iron(-I) centre.

Metallosupramolecular complexes derived from bis(benzene-o-dithiol) ligands.

Contrary to its catechol analogue, the 1,5-naphthalenediamido-bridged bis(benzene-o-dithiol) ligand H(4)-3 does not yield [Ti(4)L(6)](8-) clusters when reacted with Ti(4+) starting materials, but instead gives dinuclear, triple-stranded complexes of type [Ti(2)L(3)](4-). The molecular structures of such complexes differ depending on the size of the counterions employed. The formation of both meso complexes (Lambda,Delta or Delta,Lambda isomers) and of dinuclear triple-stranded helicates (Lambda,Lambda or Delta,Delta isomers) was observed. Molecular-modeling calculations show energetically close minima for the meso complex and the corresponding helicate. In spite of the structural differences in the solid state, proton NMR spectra reveal C(3) symmetry for all three complex anions. Metal-donor interactions mainly dictate the coordination behavior, whereas the topology of the ligand has less influence. In addition, the dinuclear complex [Ti(2)(8)(3)](4-) with the unsymmetrical bis(benzene-o-dithiol) ligand H(4)-8 has been prepared. The unsymmetrical ligand can lead to four different stereoisomers when forming dinuclear triple-stranded complexes of type [Ti(2)(8)(3)](4-), two of which have been observed in solution.

A phosphorus analogue of Bis(eta4-cyclobutadiene)iron(0).

P makes it possible: The convenient oxidative synthesis of the 16-electron organophosphorus iron sandwich complex [Fe(eta(4)-P(2)C(2)tBu(2))(2)] (see structure) suggests that the elusive all-carbon complex [Fe(eta(4)-C(4)H(4))(2)] is a viable synthetic target.

Electronic ground states of iron porphyrin and of the first species in the catalytic reaction cycle of cytochrome P450s.

Electronic structures of iron(II) and iron(III) porphyrins are studied with density functional theory (DFT) using the GGA exchange functional OPTX in combination with the correlation functional PBE (OPBE) and with the correlation functional Perdew (OPerdew) together with a triple zeta-type basis set. These functionals, known for accurately predicting the spin ground state of iron complexes, are evaluated against other functionals for their performance in calculating relative energies for the various electronic states of both the iron porphyrins. The calculated energy orderings are triplet < quintet < singlet for the iron(II) porphyrin and quartet < sextet < doublet for the iron(III) porphyrin cation. Complexation by a thiolate ion (SH-) changes the preferred ground state for both species to high spin. This thiolate complex is used as a mimic for the cytochrome P450s active site to model the first step of the catalytic cycle of this enzyme. This first step is believed to concern the removal of an axial oxygen donating ligand from the hexacoordinated aqua-thiolate-porphyrin-iron(III) resting state. The DFT results suggest that this is not a free water molecule, because of its repulsive nature, but that it has instead hydroxy anion character. These calculations are in line with the experimentally observed change in the spin state from low to high spin upon this removal of the axial hydroxo ligand by binding of the substrate in the heme pocket of cytochrome P450.

Nonplanarity at tri-coordinated aluminum and gallium: cyclic structures for X3Hn(m) (X = B, Al, Ga).

Structures and energies of X3H3(2-), X3H4-, X3H5, and X3H6+ (X = B, Al and Ga) were investigated theoretically at B3LYP/6-311G(d) level. The global minimum structures of B are not found to be global minima for Al and Ga. The hydrides of the heavier elements Al and Ga have shown a total of seven, six and eight minima for X3H3(2-), X3H(4-), and X3H5, respectively. However, X3H(6+) has three and four minima for Al and Ga, respectively. The nonplanar arrangements of hydrogens with respect to X3 ring is found to be very common for Al and Ga species. Similarly, species with lone pairs on heavy atoms dominate the potential energy surfaces of Al and Ga three-ring systems. The first example of a structure with tri-coordinate pyramidal arrangement at Al and Ga is found in X3H(4-) (2g), contrary to the conventional wisdom of C3H3+, B3H3, etc. The influence of pi-delocalization in stabilizing the structures decreases from X3H3(2-) to X3H6+ for heavier elements Al and Ga. In general, minimum energy structures of X3H4-, X3H5, and X3H6+ may be arrived at by protonating the minimum energy structures sequentially starting from X3H3(2-). The resonance stabilization energy (RSE) for the global minimum structures (or nearest structures to global minimum which contains pi-delocalization) is computed using isodesmic equations.